Originally posted by ska.one:

I beat all the bosses but Bonemass on my solo server, and Bonemass on a group server. I never got the drakes, skeleton surprise, or fulings attack my base (but fulings will spawn in the forest, for example). The non-boss events, I got Trolls enough time to have a full chest of skins, and Smell from the Swamp enough time to never need entrails ever again. My events are all jammed up.

Started a new seed, so back to the creatures of the forest uniting for Elkthyr.

That's because each boss triggers specific events. Read here for details:
https://valheim.fandom.com/wiki/Events